So after that whole myth about sex in space got thrown around and it turned out to be bunk (well, ok, I'm calling it bunk until I see the report my ownself, and I was SO happy to be able to say "sex...in...spaaaaaaaaaaaaaaaaaaace...". Blah), I figure I owe you guys some REAL Friday Weird Science. Or at least, a really amusing hypothesis.
Ah, Journal of Medical Hypotheses. Where would we be without the hilarious, half-baked meanderings of people who submit their lightly-supported ideas to a journal with no peer-review?
I would like to dedicate this post to my laboratory manager. She is totally hilarious, and went through some rough surgery for carpal tunnel a few years ago. And now she's going to go through an even MORE rough time as I mock her for the next few years about how she GOT the carpel tunnel. Mwah-ha-ha-ha...
Kudos also go out to NCBI ROFL, who pointed me towards this paper in the first place. What's up, guys. John Zenian. 'The role of sexual intercourse in the etiology of carpal tunnel syndrome' Medical Hypotheses, 2010.

Let's start with carpal tunnel. Carpal tunnel is identified by tingling and numbness in the hand and wrist, accompanied by shooting pains. This occurs the median nerve in your wrist gets squeezed, which can occur because the tendons around it are inflamed, say, by the constant angle and motion of your hands and fingers on a keyboard or wielding a pipette. It can be a painful and debilitating condition, and often requires surgery. Not fun.
Repetitive motion is the most common cause cited for the development of carpal tunnel, so in this paper, the author hypothesizes (and he's REALLY hypothesizing here) that the "repetitive motion" involved in the missionary position of sexual intercourse could be a major cause of carpal tunnel.
Where does he get this hypothesis? He went through a list of non-occupational risk factors for carpal tunnel (so not typing on the keyboard, though I suppose as a blogger where this is my hobby, my cause of carpal tunnel may indeed be non-occupational...I still prefer to blame my thesis). Risk factors that popped out to him include:

marital status

pregnancy

use of oral contraceptives

hormone supplementation

And he proposes that each of these has an association with increased frequency of sexual intercourse. The idea is that the repetitive force of levering yourself up on your arms while having sex is a risk factor for carpal tunnel. And therefore, the more sex you have, the more likely you are to get carpal tunnel. As if sex wasn't risky enough!
You will note that most of the things on that list apply to women. Women are known to get carpal tunnel more often than men, and to the author, this comes down to the fact that there are more positions in sex that rely on a girl supporting her weight on her wrists.
He additionally notes that obesity is a significant risk factor for carpal tunnel, and hypothesizes that this is because you're putting increased weight on your wrists during sex. Carpal tunnel apparently decreases after age 63, and he thinks this is because old people aren't having as much sex. Similarly, he thinks it doesn't generally occur in children and adolescents because they aren't having as much sex.
Of course this doesn't explain why incidence of carpal tunnel peaks at 40-50. You'd assume that it would occur earlier if sex really was the cause, as presumably people are having the most sex in their 20s and 30s. To explain this, the author says that younger people have better muscle tone and thus can handle the sex better.
It's really all about the sex. He notes that sex is one of the only things where your wrists are used in an "ergonomically identical" fashion, and thus this might explain the increase in bilateral carpal tunnel. He also thinks that rates of carpal tunnel have been increasing lately because of the new popularity of oral contraceptives since the 60's, which is causing women to have MORE sex, thus putting MORE pressure on their weak little wrists, and thus causing MORE carpal tunnel.
First off, I think this hypothesis for a risk factor of carpal tunnel is hilarious. One must wonder whether or not this guy has carpal tunnel...
But the amusement factor alone doth not a good hypothesis make. Here are some of my (MANY) issues with this charming three-page...waste of paper:
1) This guy honestly thinks that married people have more sex because they are more likely to have a "steady sexual partner". I'd love to see a citation on that one, but I do not think it's true. I'm not going to state the anecdote that sex goes away when you get married, because anecdotes are not data, but I would be willing to bet that, on average, married people do not have more sex than single people of the same age.
2) He thinks that pregnancy is part of this hypothesis because people who are pregnant will have had a history of sexual activity, and so they've had past strain from their baby-making practice. First off, pregnancy is associated with a TON of changes in the body, many of them hormonal, and which are known to have effects on tendons and ligaments, as well as joints, and which may present risk factors for carpal tunnel. Those changes aside, you need to also take into account that a pregnant woman is carting around a good 20 lbs of unexpected weight, and that is going to put some strain on the wrists during some activities. So I would say there are a lot of other factors putting pregnant women at risk of carpal tunnel, far more than those resulting from previous exertions.
3) He proposes the use of oral contraceptives and hormone supplementation because he believes these people (specifically women) have more sex and increased libidos, and therefore will be more at risk for sex-induced carpal tunnel. Yet again, we're dealing with people taking hormones, which could well impact ligaments and tendons. See point 2.
4) There are more sex positions in which women have to support themselves with equal weight distribution on their wrists. Really? I'd love to see that study. Also, given the preponderance of the missionary position, would not men also be at increased risk for carpal tunnel? Is there a study on carpal tunnel in women who lie there and think of England vs those who don't?
5) Finally, the one that gets me the most: the increase in carpal tunnel due to the increase in sex, which is in turn due to an increase in women taking oral contraceptives. This point completely ignores the OTHER things that people have start doing since the 60's, including a heck of a lot more driving, and a LOT more time on the computer, even in a non-occupational capacity.
And what about the MEN? Why is this increase in sexual activity among women causing extra carpal tunnel? The women have to be having sex with SOMEONE, and given marital status, pregnancy, etc, thus author is obviously assuming primarily heterosexual sex. This doesn't account for rates of carpal tunnel in men, which have also been increasing. And really, if sex is a major risk factor for carpal tunnel in both men AND women, Sci would love to see a study on rates of carpal tunnel in the dominant hand of single men vs married men.
So basically, even though a sexual theory of carpal tunnel is admittedly hilarious, Sci would have to see some pretty hard data to be really convinced. As it is, typing up this blog post made Sci's wrists hurt, and I'll let you guys speculate on the cause.Zenian, J. (2010). The role of sexual intercourse in the etiology of carpal tunnel syndrome Medical Hypotheses DOI: 10.1016/j.mehy.2009.12.015

Well, c'mon, all that knitting and crocheting of those little baby booties...
And the breast enlargement secondary to the OCPs means the laydeez must be having it off frequently despite the libicidal effects.
Yeah, this seems like another Medical Hypotheses study FAIL.
I keep wanting to come up with a drinking game based on Med Hypotheses. But what kind of nerd comes up with a drinking game based on a journal?
Note how I'm avoiding all the obvious comments about marriage and sexual activity. Mainly because I can't recall the studies, and it's late, and I have to go to bed now that I'm done reviewing the day's work. 5 hours after my spouse did. Comment reserved.

Eureka! I've got it! Climbing out of the bath causes carpal tunnel!
Actually, I think it's from all the wimminz who've read this paper, then smacked their foreheads with their palms for wondering why they never thought of this before. It's so obvious! Bwahahahaahah!
But to Sci's point: driving, typing, cracking the whip over your subordinates, cracking one off, walking the dog (physically or metaphorically), pushing away the unwanted and lascivious advances of strangers, washing dishes, ringing bells, throwing Frisbees, eating with knives and forks, playing musical instruments, doing pushups, holding crazy yoga postures, shaking the hands of all your fans and political buddies, and getting out of the bath... just to name a few.

Yeah, that's a GREAT hypothesis. Let's ignore the ways in which hormones are mediators of inflammatory processes (which is a more parsimonious explanation for the sex difference... and, you know, is right and all). Plus, isn't missionary man on top? So why would women get more carpal tunnel from that position?
And how many hours do people have intercourse, compared to the folks performing high risk activities (for carpal tunnel) in occupations where people get it a lot? I mean, I don't pipette for a few minutes a few times a week (well, now that I'm faculty, actually I don't even do it that much, but you know what I mean). I type for hours every day, etc.
Thanks for sharing this Weird Science, Sci!

The first thing that popped into my head when I started reading your article and the hints to sex were coming in was masturbation. What else is repetitive and straining using one's hands and wrists in sometimes awkward positions?
But it wasn't even mentioned!
strange...

3) He proposes the use of oral contraceptives and hormone supplementation because he believes these people (specifically women) have more sex and increased libidos, and therefore will be more at risk for sex-induced carpal tunnel. Yet again, we're dealing with people taking hormones, which could well impact ligaments and tendons.
Touche. Also, don't hormonal contraceptives also have the potential side effect of decreased libidos?

Thanks for another interesting edition of Weird Science, Sci.
Since you want a citation to increased sexual frequency among married folk, the classic study here is:
Laumann, E., Gagnon, J.H., Michael, R.T., and Michaels, S. The Social Organization of Sexuality: Sexual Practices in the United States. 1994. Chicago: University of Chicago Press
It's getting to be a bit old, but it is the biggest study of its kind. Or if you just want numbers, here they are on the Kinsey Institute website:http://www.kinseyinstitute.org/resources/FAQ.html#frequency

Carpal tunnel syndrome can actually improve solitary sex. wait till the hand loses all feeling and then off you go. It will feel like someone else is doing it.
If you don't have carpel tunnel syndrome you can get a similar effect with 2 ml lignocaine injected round the median nerve at the wrist.......................oops too much information.